Physical Unclonable Function (PUF) makes use of random process variations during manufacturing of integrated circuit to produce cipher for application to the password system. Due to random process variations, different chips of the same structure may obtain different output responses under the same excitation. The attacker is unable to clone the PUF circuit with identical output response due to uncontrollable process variations despite of the fact that the attacker knows structure of the PUF circuit. PUF circuit can defense numerous conventional attacks owing to its unclonable properties. Pappu and his colleagues proposed the concept of PUF firstly, and designed an optical PUF to realize such applications as system certification. Later, Gassend and his colleagues proposed PUF circuit based on the conception of random functions for silicon parameters. Therefore, study and application of PUF circuit have become more and more extensive, such as protection of intellectual property rights, equipment certification, hardware identification and cipher generation.
In the silicon PUF circuit, such problems as gate time delay and interconnect crosstalk brought forth by parasitic effect of interconnecting line will become more and more serious once the characteristic dimension is reduced to the nanometer scale. Uniqueness of PUF circuit represents the capability in differentiating different chips of the same structure; whereas randomness may affect the intensity of unclonable property of the circuit; therefore, it is of vital importance to improve randomness and uniqueness of PUF circuit. Carbon Nano transistor (CNT) is provided with ballistic transmission performance owing to extremely long free path of its elastic scattering. As compared with 3D silicon and Silicon-On-Insulator CNT of quasi one-dimension structure has higher electronic control capability. Carbon Nanotube Field Effect Transistor (CNFET) takes CNT as conducting channel; PUF circuit as designed based on CNFET is provided with better randomness and uniqueness. In PUF circuit, it is applicable to improve complexity of cipher by increasing the quantity of challenge-response pairs (CRPs). For binary PUF circuit, increased quantity of challenge-response pairs will inevitably increase the area of chips. As compared with binary logic ternary logic can take the signal value of “0”, “1” and “2”; for PUF circuit of the same n bit, the quantity of challenge-response pairs of ternary PUF circuit is times (1.5)n of that of binary PUF circuit.
Thus, it is of vital importance to design a CNFET based ternary PUF unit and circuit featuring in smaller area of circuit and excellent randomness and uniqueness in combination with CNFET and ternary logic technology while maintaining the correct logic functions.